Debugging

2 © 2003, Espirity Inc. Module Road Map 1.Eclipse Debugging  Debug Perspective  Debug Session  Breakpoint  Debug Views  Breakpoint Types  Evaluating and displaying expressions

3 © 2003, Espirity Inc. Debugging in Eclipse The Java Debugger  Part of Eclipse Java Development Tools (JDT)  More than System.out.println( ̎̎̎̎ error ̎̎̎̎ )  Detects errors as code executes  Correct errors as code executes  Actions you can perform debugging include:  Control Execution  Set simple breakpoints  Set conditional breakpoints  Review and change variable values  Hot code replace (feature new to JRE 1.4)

4 © 2003, Espirity Inc. Debug Perspective Threads and Monitor View Console View Outline View Editor View Tasks View Variable View

5 © 2003, Espirity Inc. Simple Breakpoint Breakpoint  Stops the execution of a program at the point  Thread suspends at the location where the breakpoint is set Setting a breakpoint  CTRL+Shift+B at current point in editor line  Double click in editors marker bar a current line

6 © 2003, Espirity Inc. Starting a Debugging Session Select Java class containing the following:  main() method  Resulting execution will pass breakpoint Select Run  Debug As…  Java Application Or Select Debug As…  Java Application from the debug menu

7 © 2003, Espirity Inc. Debug Session Execution suspends prior to the line with a breakpoint You can set multiple breakpoints

8 © 2003, Espirity Inc. Deleting Breakpoints Double click on the breakpoint in the editor

9 © 2003, Espirity Inc. Control Execution From Breakpoint… Step Into or F5:  For methods, execute method and suspend on first statement in the method  For assignments, similar to Step Over  For conditionals, similar to Step Over Step Over or F6  Execute next statement Step Return or F7  Resume execution to the end of the method on the next line after it was invoked

10 © 2003, Espirity Inc. …Control Execution From Breakpoint Resume or F8  Continue execution until program ends or another breakpoint is reached Terminate  S tops the current execution thread

11 © 2003, Espirity Inc. Variables and Fields To see the values bound to fields:  Use Variables View  Select variable in editor and select Inspect  Select variable in editor and select Display

12 © 2003, Espirity Inc. public class Debug { private int something = 0; private Vector list = new Vector(); public void firstMethod(){ thirdMethod(something); something = something + 1; } public void secondMethod(){ thirdMethod(something); something = something + 2; } public void thirdMethod(int value){ something = something + value; } public static void main(String[] args) { Debug debug = new Debug(); debug.firstMethod(); debug.secondMethod();} } Code Debugging in this Module

13 © 2003, Espirity Inc. Variables View Shows all fields of instance where breakpoint occurred  Select this to see all fields  Select any field to see value  If field is bound to an object, you can select Inspect from the menu to view its fields and values

14 © 2003, Espirity Inc. Changing Field Values To change field value:  Select field in Variables view  Select Change Variable Value from the menu  Enter new value into Set Variable Value window  Click OK

15 © 2003, Espirity Inc. Display View Displays the result of evaluating any expression in the current context Opens by:  Selecting a field in the editor or Variables View and choosing Display  Clicking on the Display tab

16 © 2003, Espirity Inc. Expressions View Remembers all objects you have inspected Displays the fields of the object  You can see the values of the fields  You can Inspect the fields Opens when:  You Inspect an object  You click on the Expressions tab

17 © 2003, Espirity Inc. Breakpoint View Lists all available breakpoints Can be used for manipulating breakpoints (through the views menu):  Enabling  Disabling  Removing Also displays breakpoints properties Accessed like other debugging views

18 © 2003, Espirity Inc. Debug View Shows:  Active threads  Current stack frame when execution has stopped  Previous stack frames Method and variables are shown in the editor for the selected frame  Update in the editor updates the source

19 © 2003, Espirity Inc. Breakpoint Types Breakpoints can be set for the following Java entities:  Line (simple breakpoint)  Method  Field (Watchpoint)  Java Exception Each breakpoint is set a different way and has different properties

20 © 2003, Espirity Inc. Method Breakpoints To set method breakpoint:  Select method in the Outline View  From context menu select Add/Remove Method Breakpoint To set breakpoint’s properties:  Select breakpoint in editor  Select Breakpoint Properties.. from context menu  Set properties as desired  Entry, exit, enable hit count Execution suspends on entry/exit into method

21 © 2003, Espirity Inc. Field Breakpoints Also known as watchpoint To set the watchpoint:  Select field in the Outline View  From context menu select Add/Remove Watchpoint To set watchpoint’s properties:  Select breakpoint in editor  Select Breakpoint Properties.. from context menu  Set properties as desired  Access/modification, enable Execution suspended on access/modification of field

22 © 2003, Espirity Inc. Java Exception Breakpoint To Add Java Exception Point:  Select Add Java Exception Point from menu  Enter exception type  Specify what triggers a breakpoint:  Caught exception  Uncaught exception  Both

23 © 2003, Espirity Inc. How To Debug Here are simple steps for debugging in Eclipse:  Set your breakpoints  Hit a breakpoint during execution  Walk/step through code to other breakpoints  Follow along in editor  Inspect/Display interesting fields  Watch the Console for things to happen

24 © 2003, Espirity Inc. Summary You have learned:  The views in the Debug Perspective  Typical debug session  How to use the Inspector  About the different types of breakpoints  How to set breakpoints  How step around your code doing debugging

25 © 2003, Espirity Inc. Labs! Lab: Debugging in Eclipse